Entamoeba histolytica is a protozoan which causes a disease known as amoebic dysentery. This protozoan can also cause abscesses in the liver. Entamoeba is transmitted in contaminated food and water by the ingestion of cysts. Infections by this protozoan are rarely deadly, although they can cause significant disease and discomfort.
Entamoeba protozoan's have a lifecycle with two distinct stages. The first stage is a cyst stage, in which he protozoan is not mobile, but is highly resistant to being killed. Entamoeba cysts are killed by boiling water, but not by exposure to chlorination. The active stage is known as the trophozoite stage. In this stage, the protozoan is capable of causing infection. Entamoeba infections are found worldwide, however they are most frequent in tropical countries. Up to 1% of the population of the United States is affected by Entamoeba protozoans. In America, this infection is most common amongst the male homosexual population.
Once ingested, the cysts enter the small intestine. From here, they develop into trophozoites which ultimately settle in the large intestine. Once settled, the Entamoeba will invade the tissues of the large intestine and begin to secrete enzymes, which will cause damage to the surrounding tissues. There is little active inflammation. However, it is possible for a small ulceration to form at the site of the infection.
Signs and Symptoms
An active Entamoeba infection will cause diarrhea. The diarrhea will often contain mucous and will commonly be streaked with some amount of blood. Diarrhea of this type is referred to in general terms as dysentery. The diarrhea will be accompanied by pain and discomfort in the abdomen, as well as flatulence. A chronic infection can often lead to weight loss and fatigue. Over 90% of people infected by Entamoeba will become carriers. These people will shed cysts in their stools, but will present with no symptoms.
On occasion, Entamoeba is capable of traveling to the liver. An Entamoeba infection of the liver can cause an amoebic abscess. An amoebic abscess will cause many nonspecific symptoms, such as pain in the upper right abdomen, weight loss, fever, and a very tender liver.
Methods of Diagnosis
In addition to taking a proper history from the patient, it is important to analyze the stool of a person with a suspected Entamoeba infection. A stool sample will show either the cysts, or the trophozoites. Differentiating Entamoeba from other protozoans can be somewhat difficult, however a properly trained microbiology lab should be capable of doing this without much trouble.
An Entamoeba infection is not a bacterial infection, and as such antibiotics are not useful. The treatment of choice for an Entamoeba infection is a medication known as metronidazole. The common brand name for this drug is Flagyl.
As with most parasites, it is best to avoid contracting the infection in the first place. As the saying goes, an ounce of prevention is worth a pound of cure. Good personal hygiene, including hand washing, especially when you suspect you may be exposed to contaminated food or water, is an essential element in preventing the spread of Entamoeba.